Even with defects, graphene is strongest material in the world

Graphene remains the strongest material ever measured and, as Columbia Engineering Professor James Hone once said, so strong that "it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap." Credit: Andrew Shea for Columbia Engineering

In a new study, published in Science May 31, 2013, Columbia Engineering researchers demonstrate that graphene, even if stitched together from many small crystalline grains, is almost as strong as graphene in its perfect crystalline form. This work resolves a contradiction between theoretical simulations, which predicted that grain boundaries can be strong, and earlier experiments, which indicated that they were much weaker than the perfect lattice.

Graphene consists of a single atomic layer of carbon, arranged in a honeycomb lattice. "Our first Science paper, in 2008, studied the strength graphene can achieve if it has no defects—its intrinsic strength," says James Hone, professor of mechanical engineering, who led the study with Jeffrey Kysar, professor of mechanical engineering. "But defect-free, pristine graphene exists only in very small areas. Large-area sheets required for applications must contain many small grains connected at grain boundaries, and it was unclear how strong those grain boundaries were. This, our second Science paper, reports on the strength of large-area graphene films grown using chemical vapor deposition (CVD), and we're excited to say that graphene is back and stronger than ever."

The study verifies that commonly used methods for post-processing CVD-grown graphene weaken grain boundaries, resulting in the extremely low strength seen in previous studies. The Columbia Engineering team developed a new process that prevents any damage of graphene during transfer. "We substituted a different etchant and were able to create test samples without harming the graphene," notes the paper's lead author, Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab. "Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications."

In its perfect crystalline form, graphene (a one-atom-thick carbon layer) is the strongest material ever measured, as the Columbia Engineering team reported in Science in 2008—so strong that, as Hone observed, "it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap." For the first study, the team obtained small, structurally perfect flakes of graphene by mechanical exfoliation, or mechanical peeling, from a crystal of graphite. But exfoliation is a time-consuming process that will never be practical for any of the many potential applications of graphene that require industrial mass production.

Currently, scientists can grow sheets of graphene as large as a television screen by using chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. One of the first applications of graphene may be as a conducting layer in flexible displays.

"But CVD graphene is 'stitched' together from many small crystalline grains—like a quilt—at grain boundaries that contain defects in the atomic structure," Kysar explains. "These grain boundaries can severely limit the strength of large-area graphene if they break much more easily than the perfect crystal lattice, and so there has been intense interest in understanding how strong they can be."

The Columbia Engineering team wanted to discover what was making CVD graphene so weak. In studying the processing techniques used to create their samples for testing, they found that the chemical most commonly used to remove the copper substrate also causes damage to the graphene, severely degrading its strength.

Their experiments demonstrated that CVD graphene with large grains is exactly as strong as exfoliated graphene, showing that its crystal lattice is just as perfect. And, more surprisingly, their experiments also showed that CVD graphene with small grains, even when tested right at a grain boundary, is about 90% as strong as the ideal crystal.

"This is an exciting result for the future of graphene, because it provides experimental evidence that the exceptional strength it possesses at the atomic scale can persist all the way up to samples inches or more in size," says Hone. "This strength will be invaluable as scientists continue to develop new flexible electronics and ultrastrong composite materials."

Strong, large-area graphene can be used for a wide variety of applications such as flexible electronics and strengthening components—potentially, a television screen that rolls up like a poster or ultrastrong composites that could replace carbon fiber. Or, the researchers speculate, a science fiction idea of a space elevator that could connect an orbiting satellite to Earth by a long cord that might consist of sheets of CVD graphene, since graphene (and its cousin material, carbon nanotubes) is the only material with the high strength-to-weight ratio required for this kind of hypothetical application.

The team is also excited about studying 2D materials like graphene. "Very little is known about the effects of grain boundaries in 2D materials," Kysar adds. "Our work shows that grain boundaries in 2D materials can be much more sensitive to processing than in 3D materials. This is due to all the atoms in graphene being surface atoms, so surface damage that would normally not degrade the strength of 3D materials can completely destroy the strength of 2D materials. However with appropriate processing that avoids surface damage, grain boundaries in 2D materials, especially graphene, can be nearly as strong as the perfect, defect-free structure."

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19 comments

This sounds like an ideal material to make an orbital airship out of. If we forget about using it as a re-entry vehicle the promise is $1 per tonne per mile lifted. This makes Gerard K O'Neil's vision much more practical. With a 35 year doubling time for the population we need habitats at L4 and 5. The habitats too need to be wrapped up in this material to withstand the 9.8N per kg created by the artificial gravity.

Why? This is a serious question: why do we need habitats in space? There's no way to make them self sufficientAnd why exactly would we want them at L4 and L5 (as opposed to in orbit around planets/moons or on asteroids or just in their own orbit around the sun)?

Humans aren't adapted to life in space. But when we get to the point of adapting ourselves to life in space (which probably means transferring into some hardy other type of body - or going fully virtual) then there's no need for habitats at all.

If graphene is like many other materials, the cost will increase exponentially with the level of purity. Just like horsepower ratings, purity levels claimed by the marketing department are always suspect and difficult to verify.

If strength is largely unaffected by impurities, the cost of goods made with graphene should be very low. Just laminate a few inexpensive, impure layers together and it will likely be "strong enough".

Why? This is a serious question: why do we need habitats in space? There's no way to make them self sufficientAnd why exactly would we want them at L4 and L5 (as opposed to in orbit around planets/moons or on asteroids or just in their own orbit around the sun)?

Humans aren't adapted to life in space. But when we get to the point of adapting ourselves to life in space (which probably means transferring into some hardy other type of body - or going fully virtual) then there's no need for habitats at all.

"O'Neill's first published paper on the subject, The Colonization of Space, appeared in the magazine Physics Today in September 1974. A number of people who later became leaders of the L5 Society got their first exposure to the idea from this article. Among these were a couple from Tucson, Arizona, Carolyn and Keith Henson." etc

The L5 society. Lead by a writer and ex-engineer and another writer who doesn't even know her stuff. Really? That's your fabulous group?

I mean...seriously?

No you dont mean seriously. If you did you would have read the link.

"Gerard Kitchen O'Neill (February 6, 1927 – April 27, 1992) was an American physicist and space activist. As a faculty member of Princeton University, he invented a device called the particle storage ring for high-energy physics experiments. Later, he invented a magnetic launcher called the mass driver. In the 1970s, he developed a plan to build human settlements in outer space, including a space habitat design known as the O'Neill cylinder. He founded the Space Studies Institute, an organization devoted to funding research into space manufacturing and colonization."

"Space Studies Institute is a non-profit[2] organization that was founded in 1977 by the late Princeton University Professor Dr. Gerard K. O'Neill. The stated mission is to "open the energy and material resources of space for human benefit within our lifetime".

In 2009 SSI moved its operations from its long-term base in Princeton, New Jersey, to Mojave, California. SSI is involved in several initiatives, including a solar sail project that it is developing with Carnegie Mellon University and an effort to find asteroids that could be mined for valuable materials. The use of extraterrestrial resources in space settlement has been an area that has received very little attention in recent years."

-Ever hear of it? He also taught here

"Princeton University is a private research university located in Princeton, New Jersey, United States. It is one of the eight universities of the Ivy League..." etc

Yes, so? It's a pretty quaint concept - devoid of any kind of relation to what humans (i.e. their biology) requires. And not entirely in touch of what we're currently (or in the foreseeable future) able to do, either.

It's cool science fiction (BTW: he didn't even invent it. He grabbed the idea from a publication by Hermann Oberth in the 50's and the Novel "Rendezvous with Rama" by Arthur C Clarke in the early 70s)

The L5 society are right up there with the guys that want to build a real starship enterprise. Cool idea - complete lack of any kind of reality check.

Both sides here are making valid points, but I agree with antialias on this one. America, the richest nation EVER, can't even feed it's own citizens. Something like 1 in 6 Americans go hungry at least some of the time. This is a civilization that lacks the willpower to feed innocent children, why would it invest in a technology that would cost thousands of times more per capita to keep people alive? Even if it did happen, it would not end up as the utopia claimed by its supporters, it would be corrupted like every other human enterprise. Wait for Matt Damon's new Sci-fi movie Elysium, then you'll see what that technology will really do for humanity. We don't deserve to have access to the resources of the solar system, not until we take to heart the lessons about what it means to be human. Our civilization is like the superhero Hancock, all potential and no follow through. We can do better, we must do better. It starts at home, the Earth.

Oh sorry AA anyone who is familiar with the work that has been done on space colonization knows of the significance of dr o'neills work. Which is not you, since you were clueless (again) until I called you on it.

Clarke wrote informed fiction but Oneill did the Physics, telling us where and how it could be built using material shot from the moon using mass drivers which he also invented.

If you do a little more fevered post hoc research you may discover why he and others thought that L5 was an ideal spot.

A geologist can do alot more with curiousity by his/her side than curiosity alone.

Such as?You have to always keep this in perspective. A geologist on the spot can do very little that a robot can't. The geologist can do very little without any tools. And whether you then have these tools on a robot and beam back the info or have the guy operate the tools on the spot makes no difference.

Add to that that the expense of getting a human (and maintaining him in any kind of shape) on Mars is immense.Not to mention that a robot can stay for a very long time compared to a human.

So unless we figure out how to make space travel for humans a lot cheaper robots are our best bet.

Did you know that some 50% of pregnancies in the US are unintended? When will we have the willpower as a culture to address the cause of hunger? When will the species be mature enough to take a stand and restrict religions from forcing women to drop babies until it kills them?

In the meantime we have other issues to address. Overpopulation could well cause species collapse within the next few gens. Unemployment approaches 50% in Spain, Greece, and Italy for those under 25. This is growth beyond the means to support itself.

We need to disperse the species throughout the inner system, starting with mars, so that it won't die out.

Who here doesn't like dan brown? Too bad. His latest book is all about overpopulation and what it could lead to. It's NOT going to fix itself. It WON'T go away. And it WILL end us if something is not done SOON.

Why are al qaida and the Taliban winning? They have an Endless supply of cannon fodder.

Did you know that some 50% of pregnancies in the US are unintended? When will we have the willpower as a culture to address the cause of hunger? When will the species be mature enough to take a stand and restrict religions from forcing women to drop babies until it kills them?

In the meantime we have other issues to address. Overpopulation could well cause species collapse within the next few gens. Unemployment approaches 50% in Spain, Greece, and Italy for those under 25. This is growth beyond the means to support itself.

Pretending this problems are being solved by the speeches & pontificating the "honorables" we elect to deal them is not getting us any closer to solving them. I agree they are drastic problems & like climate,, talking only feels like working on them.

We need to disperse the species throughout the inner system,.

I am all for space exploration. But as far as saving humanity,,,, I don't think that is where we get the most return for the expenditure.

Sorry but that's because you are unaware of the extent of the imminent danger the species is in. Brown suggests that an endemic virus can be concocted which would sterilize 1/3 of every generation genetically; implying that it could just as easily sterilize everybody.Sci fi? Now? Tomorrow? How many species-ending threats can you think of? Guaranteed there are many many more. And overpopulation is perhaps the biggest.

The Only Way to save us is to disperse us. Now. New colonists need not bring these destructive religionist cultures with them. It will be a new and completely independent start.

As an alternative we can construct totally independent colonies underground, and this may have already been done. But we would still all be in one spot and vulnerable to impacts and perhaps from pathogens in ground water.

America, the richest nation EVER, can't even feed it's own citizens. Something like 1 in 6 Americans go hungry at least some of the time. This is a civilization that lacks the willpower to feed innocent children,

I don't believe any part of this statement.

America has more than enough food to feed their citizens. If someone in America is hungry, it's because they are too lazy or too proud or too stupid to find the soup kitchens. In America, there's a sugar-tit for everyone who wants/needs one.

The Only Way to save us is to disperse us. Now. New colonists need not bring these destructive religionist cultures with them. It will be a new and completely independent start."

IMHO, these ideas are true. There remain many severe problems, such as (1) getting off this spec of a planet. The graphene tether seems like a great idea, if the engineering can make it work. Say this takes 50 years. (2) Next, we need a place to go. The Earth is in the"Goldilocks" zone of our solar system, and nothing else is, so perhaps: a. Mars can be terraformed. Say this takes 100 years.b. We go to an exo-planet. Say this takes 1000 years.

==> The prospects are 12 Billion people by 2050. (37 years)

The Communist Atheist Chinese limited families to one child. Anyone want to do that?

The Communist Atheist Chinese limited families to one child. Anyone want to do that?

The chinese are still dealing with a recalcitrant relligionist culture which has thrived on forced reproduction. Communism was INVENTED as an extreme method of destroying these cultures.

Once religion is effectively mitigated, western culture can provide the people with healthy alternatives to reproduction. We are watching this happen in china. We saw it take place in vietnam and many other places.

Religions use the "Four Horsemen of the Apocalypse"?

The most successful religions were the ones which were better at outgrowing and overrunning their neighbors. These are the only ones that are left. This is evolution of the fittest.

ONE BILLION ABORTIONS have taken place since the religionist cultures which would have prevented them were destroyed in the world wars.http://www.johnst...tion/#SU

-This alone has prevented nuclear war in the world.

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